The renin-angiotensin system is involved in the homeostatic function to control systemic blood pressure, the volume of body fluid, balance among the electrolytes, etc., associated with the aldosterone system. Development of angiotensin II converting enzyme inhibitors (ACE inhibitor) (this converting enzyme produces angiotensin II which possesses a strong vasoconstrictive action) has clarified the relation between the renin-angiotensin system and hypertension. Since angiotensin II constricts blood vessel to elevate blood pressure via the angiotensin II receptors on the cellular membranes, angiotensin II antagonists, like the ACE inhibitor, would be useful in treating hypertension caused by angiotensin.
It has been reported that various angiotensin II analogues such as saralasin, [Sar1,Ile8]A II, and the like, possess potent angiotensin II antagonist activity.
It has, however, been reported that, when peptide antagonists are administered parenterally, their actions are not proiongea and, when administered orally, they are ineffective (M. A. Ondetti and D. W. Cushman, Annual Reports in Medicinal Chemistry, 13, 82-91 (1978)).
It would be highly desirable to develop a non-peptide angiotensin II antagonist which overcomes these drawbacks. In the earliest studies in this field, imidazole derivatives having angiotensin II antagonist activity have been disclosed in Japanese Patent Laid Open No. 71073/1981; No. 71074/1981; No. 92270/1982; No. 157768/1983; U.S. Pat. No. 4,355,040, U.S. Pat. No. 4,355,040, etc. Later, improved imidazole derivatives are disclosed in European Patent Laid Open No. 0253310, No. 0291969, No. 0324377, Japanese Patent Laid Open No. 23868/1988; and No. 117876/1989. Further, pyrole, pyrazole, and triazole derivatives are disclosed as angiotensin II antagonists in European Patent Laid Open No. 0323841, and Japanese Patent Laid Open No. 287071/1989.
U.S. Pat. No. 4,880,804 discloses benzimidazole derivatives having an angiotensin II receptor antagonistic action, which are intravenously active in vivo in rats with renal hypertension. Examples of such benzimidazole derivatives are those represented by the following formula (A): wherein substituents, for example, in the 5- and/or 6-position are hydroxymethyl, methoxy, formyl, chloro, or carboxy. Although most compounds among those exemplified are orally inactive, it is said that only the 6-hydtoxymethyi and 6-chloro compounds are orally effective (100 mg/kg or less). It is, however, believed that the activity of even these disclosed compounds is insufficient for clinical uses.